From 7df71f31ae70f0d6e4e6c7511f5ba35c2977af5e Mon Sep 17 00:00:00 2001
From: Ryan Petrello <lists@ryanpetrello.com>
Date: Wed, 25 Jun 2014 17:52:06 -0400
Subject: Serialize WebOb errors as JSON if the client requests it via an
 Accept header.

Change-Id: I32040eff4259daf7a0e58b81ce861758d1d14bd9
Fixes bug 1324134
---
 pecan/core.py            | 21 ++++++++++++++++++---
 pecan/tests/test_base.py | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 3 deletions(-)

diff --git a/pecan/core.py b/pecan/core.py
index eb3fe69..0cfb3eb 100644
--- a/pecan/core.py
+++ b/pecan/core.py
@@ -1,7 +1,7 @@
 try:
-    from simplejson import loads
-except ImportError:             # pragma: no cover
-    from json import loads      # noqa
+    from simplejson import dumps, loads
+except ImportError:  # pragma: no cover
+    from json import dumps, loads  # noqa
 from itertools import chain
 from mimetypes import guess_type, add_type
 from os.path import splitext
@@ -585,7 +585,22 @@ class PecanBase(object):
         except Exception as e:
             # if this is an HTTP Exception, set it as the response
             if isinstance(e, exc.HTTPException):
+                # if the client asked for JSON, do our best to provide it
+                best_match = acceptparse.MIMEAccept(
+                    getattr(req.accept, 'header_value', '*/*')
+                ).best_match(('text/plain', 'text/html', 'application/json'))
                 state.response = e
+                if best_match == 'application/json':
+                    json_body = dumps({
+                        'code': e.status_int,
+                        'title': e.title,
+                        'description': e.detail
+                    })
+                    if isinstance(json_body, six.text_type):
+                        e.text = json_body
+                    else:
+                        e.body = json_body
+                    state.response.content_type = best_match
                 environ['pecan.original_exception'] = e
 
             # if this is not an internal redirect, run error hooks
diff --git a/pecan/tests/test_base.py b/pecan/tests/test_base.py
index c076139..b69f824 100644
--- a/pecan/tests/test_base.py
+++ b/pecan/tests/test_base.py
@@ -8,6 +8,7 @@ else:
     import unittest  # pragma: nocover
 
 import webob
+from webob.exc import HTTPNotFound
 from webtest import TestApp
 import six
 from six import b as b_
@@ -760,6 +761,42 @@ class TestControllerArguments(PecanTestCase):
         assert r.body == b_('eater: 10, dummy, day=12, month=1')
 
 
+class TestDefaultErrorRendering(PecanTestCase):
+
+    def test_plain_error(self):
+        class RootController(object):
+            pass
+
+        app = TestApp(Pecan(RootController()))
+        r = app.get('/', status=404)
+        assert r.status_int == 404
+        assert r.content_type == 'text/plain'
+        assert r.body == b_(HTTPNotFound().plain_body({}))
+
+    def test_html_error(self):
+        class RootController(object):
+            pass
+
+        app = TestApp(Pecan(RootController()))
+        r = app.get('/', headers={'Accept': 'text/html'}, status=404)
+        assert r.status_int == 404
+        assert r.content_type == 'text/html'
+        assert r.body == b_(HTTPNotFound().html_body({}))
+
+    def test_json_error(self):
+        class RootController(object):
+            pass
+
+        app = TestApp(Pecan(RootController()))
+        r = app.get('/', headers={'Accept': 'application/json'}, status=404)
+        assert r.status_int == 404
+        json_resp = json.loads(r.body.decode())
+        assert json_resp['code'] == 404
+        assert json_resp['description'] is None
+        assert json_resp['title'] == 'Not Found'
+        assert r.content_type == 'application/json'
+
+
 class TestAbort(PecanTestCase):
 
     def test_abort(self):
-- 
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